Load limiting mechanisms are known in general from various applications in motor vehicles. Steering wheels are known, for example, which plunge in the case of an accident through the impact of an occupant, and comprise a mechanism for energy absorption by means of which the energy acting one the passengers is limited. Further, resilient deformation elements are provided in the entire vehicle structure through which the energy in the event of an accident is dissipated so that the energy acting on the passenger compartment is limited.
Further, it is known to provide load limiting elements in safety belts by means of which the energy acting on the occupants during their forward displacement is limited by means of a load limiting mechanism. For this, two-part belt retractor shafts, in particular with a torsion rod arranged between both parts of the belt shaft, have proven to be effective in practice. In the event of an accident, a part of the belt shaft is then locked to the vehicle, while the respective other part is connected with the safety belt and rotates in the belt extraction direction. During the relative rotation of both parts to one another, the torsion rod arranged between both parts is plastically deformed around the its own axis thereby dissipating energy, whereby the energy in the safety belt and force exerted on the occupant during the forward displacement of the occupant is correspondingly limited. The load limiting level determined through the characteristics of the torsion rod and cannot be changed.
From WO 2006/108451 A1, which stems from the Applicant, an improved load limiting system is known. The load limiting system described therein is formed from two parts moving relative to one another, whose movement to one another is controlled by a mass system oscillating with a predetermined frequency. The dissipation of energy thereby results by alternately delaying and accelerating the parts, whereby the frequency of oscillation is almost independent from the impacting force. Thereby, different load limiting levels can be realized with this load limiting system in response to the mass of the displaced parts and the vehicle deceleration occurring in the dangerous situation, whereby the frequency and the path of the forward displacement is approximately constant.